Update on Single-Board Computers

This article takes a quick look at some of the key issues driving SBC market fragmentation and zooms in on the gap between PC/104 and EBX and the expanding realm of tiny all-in-one SBCs.

In the March/April 2001 issue of
Embedded Linux Journal (``All about
Linux-friendly Single-Board Computers''), I traced the history of
the embedded single-board computer (SBC) market from the early 80s
to the year 2000. One interesting phenomenon during that period was
the emergence and proliferation of the embedded PC architecture,
which manifested in several popular form factors, including PC/104,
EBX and passive backplane PC/PCI (refer to the March/April 2001
article for details).

A year ago, I identified five factors that were beginning to
disrupt the embedded SBC market status quo:

Exploding demand for embedded intelligence--the
universal demand that even the tiniest and least-expensive devices
have at least rudimentary embedded intelligence. Many must also
provide user-friendly graphical/touch or sound/speech
interfaces.

Evolving peripheral and bus interfaces--although
popular interconnection standards can sometimes seem immortal
(consider Centronics and RS-232), new interfaces gradually supplant
the old. Two decades after the birth of the PC, the ISA bus has
finally (mostly) been replaced by PCI. USB is now replacing the
venerable serial, parallel and PS/2 ports (PS/2 already replaced
the earlier keyboard/mouse ports). Ethernet is everywhere. SCSI has
gained popularity in server-like systems, but remains second fiddle
to IDE for hard drives and CD-ROMs. FireWire (IEEE-1394) has yet to
catch fire outside of specialized apps (mostly video) and Apple's
desktop systems, but time will tell.

Application-oriented system-on-chip
processors--numerous highly integrated ARM, MIPS, PowerPC and
x86-based one-chip systems have emerged to address the needs of a
range of high-volume and cost-sensitive products and applications.
More than ever, these ``application-on-chip'' processors represent
tantalizing fodder for the next generation of high-integration,
high-performance and highly cost-effective SBCs. Significantly,
most of these SOCs have abandoned x86 compatibility for the sake of
cost/power/integration benefits.

Embedded Linux--multiple market studies during 2001
and 2002 report that embedded Linux now ranks among the top three
OSes for new embedded projects (the top three generally include
VxWorks, embedded Linux and Windows CE/NT Embedded, in various
ranking orders). Of course, this great success for embedded Linux
comes as no surprise, given its openness, scalability, reliability,
freedom from royalties, built-in networking/internet stack,
excellent GUI/windowing support and the fact that it is available
from many vendors (with support) or freely downloadable.

One year down the road, these factors appear to have not only
continued, but to have accelerated. As a result, the embedded SBC
market continues on a path toward even greater diversification and
fragmentation.

Factors Driving Fragmentation in the Embedded
SBC Market

With the growing availability of application-oriented
system-on-chip processors, SBC vendors are beginning to target
their boards at specific applications or classes of applications.
For example, there are boards with two or more Ethernet ports that
are intended for firewall/router uses or small palm-sized boards
with built-in LCD controllers and touch input controllers for
specialized handheld computer apps.

On the other hand, the wide variation of applications in the
embedded market makes it important to have modular expandability,
not just high integration of functions, because hardly any two
applications have precisely the same requirements. Consequently,
the SBC market has evolved into three categories of
products:

Modular building blocks: standard form factor SBCs
that plug in to passive backplanes (e.g., passive backplane PC/PCI,
CompactPCI, VME) or stack directly on top of each other (e.g.,
PC/104 and PC/104-Plus).

Figure 1. PC/104 Modules Stack without Backplanes

All-in-one SBCs: they contain most or all of the
embedded computer functions, but often provide a means of
customization via either a PC/104(-Plus) expansion location or
slots for adding PCMCIA or CompactFlash Type II cards.

Figure 2. An EBX Form Factor PowerPC-Based SBC from Motorola

Macrocomponent-like SBC modules that contain the
core embedded computer functions and plug in to
application-specific baseboards like large chips. The interesting
thing here is that whereas you normally think of plugging
application-specific I/O circuitry into an SBC, in this case you
are plugging the SBC into the application-specific I/O.

Figure 3. Adastra's ETX Modules Plug onto Custom Circuit Boards

While there are some well-established standards in the SBC
market, such as EBX, PC/104, CompactPCI, PMC and the venerable
passive backplane ISA/PCI, there are a few gaps and opportunities
where new standards may emerge.